1. Field of the Invention
The subject invention relates to window wiper systems and, more particularly, to apparatus for controlling the motion of a motor-driven wiper blade used in such systems.
2. Description of Related Art
Thermal vision systems capable of producing real time video pictures in total darkness have recently been introduced for civilian use, most particularly for law enforcement agencies. Such systems work much like the forward-looking infrared technology used by the U.S. military. Current Night Vision System designs depend on clear infrared vision through an edge-heated sensor window mounted flush with a housing.
Surface quality of such a detector window must be maintained by keeping the surface free of rain and snow. Conventional "window wiper" designs for windshields are large and heavy and controlled by complex mechanical means, and are unsuitable for the compact environment of a Night Vision infrared sensor. Designs for other smaller surfaces, such as head lamps, are equally complex.
In copending application Ser. No. 08/263,272, a streamlined, small scale window wiper is disclosed which is ideally suited to remove foreign particles from an infrared detector window and thus maintain image quality during adverse environmental conditions. The wiper includes a wiper hub, wiper arm, wiper blade holder, and torsion spring means. Means for controlling the window wiper oscillating motion across the thermal imaging window is also provided. In one embodiment, such control is achieved through the incorporation of a suitable motor, Hall effect sensors, and an activating magnet. In a second embodiment, such control is achieved through the incorporation of a motor, LED sensors, and a solid disk interrupt.
In such a system, the inventors have found that problems arise when the motor which drives the wiper blade reverses direction. Electrically, a voltage spike is generated, which creates electrical wear and tear and may damage motor windings and reduce motor life. Mechanically, a backlash is created when direction is instantaneously reversed, which can stress and ultimately break gear teeth.